The present invention relates to electroless plating of substrates, and, in particular, to electroless plating of non-conductive substrates.
It is known in the prior art to electroless plate non-conductive substrates of electronic equipment in order to reduce electromagnetic radiation interference and radio frequency interference. In general, the surface of a non-conductive substrate is coated with a catalyst solution and then immersed into an electroless plating solution. The catalyst solution renders the coated surface catalytic to deposition of the plating metal.
In one prior art process, discussed in U.S. Pat. No. 5,288,313, the disclosure of which is incorporated hereby, in its entirety, by reference, the catalyst solution is a film-forming resin containing, among other things, a reduced noble metal salt. For purposes of reference herein, a noble metal is a metal that resists oxidation, such as gold, platinum, and palladium. In another prior art process, discussed in U.S. Pat. No. 4,663,240, the disclosure of which is incorporated hereby, in its entirety, by reference, the catalyst solution is an organic binder containing, among other things, a heavy metal. For purposes of reference herein, a heavy metal is a metal whose specific gravity is greater than 5, such as iron (7.894), cobalt (8.9), nickel (8.9), copper (8.96), silver (10.5), palladium (12.02), gold (19.32), and platinum (21.45).
However, a coating formed with a catalyst solution using a heavy metal is rough in appearance and, as a result, does not adhere well to the surface of the non-conductive substrate. In addition, a catalyst using a heavy metal has substantial precipitation, in other words, the heavy metal separates or xe2x80x9csettles outxe2x80x9d of the solution. Moreover, heavy metals are a cause of environmental pollution and, thereby, require special handling procedures.
In accordance with one aspect of the invention, a composition for coating a surface of a non-conductive substrate, the coated surface to be plated with a metal, the composition comprises between approximately 30% by weight and approximately 70% by weight of a binding solution, between approximately 2% by weight and approximately 10% by weight of carbon black powder, and between approximately 25% by weight and approximately 50% by weight of aluminum powder.
In an alternate embodiment of this aspect of the invention, a composition for coating a surface of a non-conductive substrate, the coated surface to be plated with a metal, the composition comprises approximately 50% by weight of a water-born binding solution, approximately 5% by weight of carbon black powder, approximately 25% by weight of aluminum powder, and water.
In alternate embodiments of these inventions, the binding solution may be a solvent-born binding solution, such as a lacquer resin, a vinyl resin, or an enamel resin, or it may be a water-born binding solution, such as a latex resin or an enamel resin. In still other alternate embodiments of these inventions, the binding solution may be clear in color, the carbon black powder may be a carbon black powder with a particle size of between approximately 1 micron and approximately 2 microns, the aluminum powder may be at least 99.0% pure aluminum powder, and the aluminum powder may be an aluminum powder with a particle size of between approximately 2 microns and approximately 3 microns.
In a further embodiment of these inventions, the coating composition may include a reducing agent for the binding solution. In a still further embodiment of these inventions, the coating composition is allowed to stand at least 2 hours prior to use.
In accordance with another aspect of the invention, a composition for plating a surface of a non-conductive substrate, the surface coated with a coating composition, the composition comprises between approximately 5% by volume and approximately 20% by volume hydrofluoric acid, between approximately 4% by volume and approximately 6% by volume plating metal, and water. In an alternate embodiment of the invention, the composition comprises between approximately 5% by volume and approximately 20% by volume phosphoric acid, between approximately 4% by volume and approximately 6% by volume plating metal, and water. The plating metal may be copper, nickel, or gold.
In accordance with still another aspect of the invention, a process for plating a surface of a non-conductive substrate with a metal, the process comprises coating the surface with a binding solution composition, the binding solution composition comprising between approximately 30% by weight and approximately 70% by weight of a binding solution, between approximately 2% by weight and approximately 10% by weight of carbon black powder, between approximately 25% by weight and approximately 50% by weight of aluminum powder, cleaning the coated surface, and immersing the cleaned, coated surface into a plating bath, the plating bath comprising between approximately 5% by volume and approximately 20% by volume hydrofluoric acid, between approximately 4% by volume and approximately 6% by volume copper sulfate, and water.
In an alternate embodiment of this aspect of the invention, a process for plating a surface of a non-conductive substrate with a metal, the process comprises coating the surface with a binding solution composition, the binding solution composition comprising approximately 50% by weight of a water-born binding solution, approximately 5% by weight of carbon black powder, approximately 25% by weight of aluminum powder, and water, cleaning the coated surface, and immersing the cleaned, coated surface into a plating bath, the plating bath comprising between approximately 5% by volume and approximately 20% by volume hydrofluoric acid, between approximately 4% by volume and approximately 6% by volume copper sulfate, and water.
In a further embodiment of these inventions, prior to the process of coating a surface of the non-conductive substrate, the surface of the non-conductive substrate may be pre-cleaned. In a still further embodiment of these inventions, the plated surface may be rinsed with water subsequent to the plating process.
In alternate embodiments of these inventions, the surface of the non-conductive substrate may be coated with the binding solution composition using a spray gun, the coated surface may be plated with the plating metal to a thickness of approximately 80 micro-inches single-sided, or the coat surface may be plated with the plating metal to a thickness of approximately 40 micro-inches double-sided. In further alternate embodiments of these inventions, the coated surface may be cleaned with a cleaner having a pH between approximately 6 and approximately 7, or the coated surface may be cleaned with an ultrasound cleaner.
In accordance with yet another aspect of the invention, a process for selectively plating a non-conductive substrate with a metal, the non-conductive substrate having been masked, the process comprises coating the surface with a binding solution composition, the binding solution composition comprising between approximately 30% by weight and approximately 70% by weight of a binding solution, between approximately 2% by weight and approximately 10% by weight of carbon black powder, between approximately 25% by weight and approximately 50% by weight of aluminum powder, cleaning the non-conductive substrate, and immersing the cleaned, non-conductive substrate into a plating bath, the plating bath comprising between approximately 5% by volume and approximately 20% by volume hydrofluoric acid, between approximately 4% by volume and approximately 6% by volume copper sulfate, and water.